The Strategic Dynamics of Cooperation in Primate Groups

The evolution of cooperation has played an important role in evolutionary biology over the last 40 years. There is a broad consensus thatHamilton’s theory of kin selection (Hamilton, 1964) provides a basis for understanding the deployment of altruism among relatives in a wide range of animal taxa (Crozier and Pamilo, 1996; Dugatkin, 1997; Emlen, 1997; Sachs et al., 2004). In contrast, there is considerably less agreement about the evolutionary processes that regulate the distribution of benefits to nonrelatives. Although Trivers (1971) introduced the theory of reciprocal altruism nearly 35 years ago, researchers have produced relatively few examples of reciprocal altruism in nature (Dugatkin, 2002; Hammerstein, 2003; Noë, 2005, 2006). Even the most carefully documented examples, such as predator inspection in schooling fish (Milinski, 1987) and egg‐trading in simultaneous hermaphrodites (Fisher, 1988), have been disputed (Connor, 1992, 1995; Dugatkin, 1997; Hammerstein, 2003; Sachs et al., 2004). This has led some researchers to focus on other processes, such as by‐product mutualism, group augmentation, and market forces, to explain the evolution of cooperation among nonrelatives (Clutton‐Brock, 2002, 2005; Connor, 1986, 1992, 1995; Kokko et al., 2001; Noë, 2005, 2006). Here I consider the nature of cooperation among nonkin in nonhuman primate groups, concentrating on evidence for turn‐taking, collaboration, and coordination. Nonhuman primates are an appropriate group of animals to focus on for several reasons. First, nonhuman primates (primates, hereafter) perform a variety of services on behalf of other group members. They groom one another; provide support in agonistic encounters; collectively defend